Low temperature stability of synthetic lubricants



\ 2,911,368 I Low TEMPERATURE STABILITY oF' SYNTHETIC LUBRICANTS.

Benjamin T. Fowler and Michael F. Hoare, Abingdon, and Hans G. 'Krischai, Oxford, England, assig'nors. to

Esso Research and Engineering Company, a corpora- --tion -of Delaware No Drawing. Application September 29, 1954 Serial N0. 459,204

7 Claims priority, application Great Britain October20, 1953 Claims. (Cl. 252-34) This invention relates to a compositionv adapted to "lubricate aviationgas turbineengines, in particular it relates to lubricating compositions containing a substan- -tial proportion of-synthetic lubricant.

Broadly speaking, the properties required for an aviation turbine lubricant are good high temperature stability, good viscosity temperature characteristics, and load carrying ability, and the coupling of a low viscosity at low temperatures with a low vapour pressure at high temperatures; These qualities are not simultaneously available from any economically attractive refining process applied to a petroleum oil.

However, 'it has previously been suggested that com- ,positions approaching these characteristics may be formulated by using a major proportion of certain synthetic esters, in particular diesters and complex esters or blends of the two can be found having properties approaching I-thosedesired.

The preferred synthetic lubricant base used in thisv invention contains a major proportion of compounds having the following structural formulae:

-R OOCR COOR R OOCR COOR OOCR R COOR OOCR' R (OOCR COOR ),,OOCR COOR R COOR (OOCR COOR' OOCR' In all the above formulae R and R' are the. residues of dicarboxylic acids: HOOCR COOH. R and K are ithe residues of monohydric alcohols: R OH. R and E'RQ, are the residues of monocarboxylic acids: RgCOOH. 'rR and R are the residues of glycols: HOR;OH. n is -monocarboxylic acids arepreferably aliphatic acids having up to 22 carbon atoms. The glycols are preferably members of the alkylene or polyalkylene glycol series, particularly useful being the polyethyleneglycolsfrom diethylene glycol up to decaethylene glycol, or diols of -the. formula (HO(CH ).,,OH where n is from'3 [012. I The molecular weight-and structure of theesters'should be such=that the resulting composition has a viscosity ,betweenl es. and 20 cs., preferably-3 to 10, at 210 F.

' "One disadvantage that has been experienced from the use;of lubricating blends based on esters, particularly 'those containing complex esters in an amount above about 20% by volume, is that they exhibit a tendency to thicken on storage at low temperatures. The reason for L a number from 1 to 6 which need not necessarily be in-' Q are those containing'about"1% or 2% additive.

additive used must be soluble in the lubricant andmust thickening is not clearly understood, 'butit is unride or acetate.

and guanidine acetate, thelast three being datented Nov. 3, 1959 .R and R are each. eitherahydroxytgrouma mercaptan group, .an-aminegroup or a carboxylic acid group, 0, m

-or.p substituted, and 'where thewxygen, sulphur or nitrogen atoms of the two substituent groups R and R may form the heterocyclicatoms in a hetero ring joining two o-carbon atoms in the aromatic nucleus Ar and where any or all the said groups .may. be substituted .by. other' groups such as alkyl amineand amide'groupsable' to,

stabilize the loW-temperatureviscosity characteristics": of lubricating oils based on syntheticesters.

'The strong organic base-preferably has the general formula:

wherein R', R" and R'" are aliphatic'hydrocarbon groups or hydrogen; the groups desirably have not morethan 10 carbon atoms, particularly not more than 4..carbon atoms. A particularly preferred organic baseisgua'nidine. i

Other salts whichmay. be used include the quaternary ammonium salts having thegeneral formula:

groups each. containingpreferably not more than 10 .car-

bon atoms, particularly not more than 4 carbon atoms, and X is an anion, preferably carbonate, sulphate chlo- Examples of compounds within the scope of this invention are catechol, hydroquinone, o-arninothiophenol,

'o-amino phenol, benzoxazole, mercaptobenzthiazole, 1,4,2,benzoxazine, phenothiazine, thianthrene, quinoxaline, resorcinol, pyrogallol, ethyl salicyclate, monoor di-butyl salicylate, monoor di-butyl phthalate, salicyl anilide, NN' di-t-butyl p-phenylene diamine, 2,3,dihydroxynaphthalene, and the corresponding naphthalene derivatives, and guanidine carbonate, guanidine sulphate guanidine salts of oxy acids.

Thus this invention comprises a lubricant composition consisting essentially of an ester type lubricant of the type hereinbefore described and a minor and fractional proportion of an additive compound of "the formula Ar(R )R as defined above. The present invention also comprises adding a small percentageof a salt 0f-a strong organic base, preferably an oil-insoluble salt-of a strong organic-base to a synthetic lubricating oil composition, particularly a composition comprising a blend-of a complex-ester and a di-ester,- heating the mixture to a temperature above C. and filtering the reaction mixture.

The proportion of the material used depends some- Generally speaking, the amount between .l% and 5%. Particularly useful compositions The not itself be precipitated at any temperature'likely to be encounteredby the lubricant inservice.

'The following tables exemplify the efficacy of the additives used in this invention. In the first table a lubricant having the composition:

20 parts by weight complex ester from sebacic acid,

Z-ethyl hexanol and polyglycol 200.

20 parts by weight dioctyl sebacate.

60 parts by weight dinonyl sebacate. +3.7 parts by .weight Acryloid 710 (poly methacrylate ester).

was used as the base oil. 7 l

In the second table the lubricant had the composition:

20% complex ester* sample D 20% DOS e 60% DNS I +3.85% Acryloid 710 +1% purified phenothiazine From sebacie acid, 2-ethy1 hexanol and Polyglycol 200.

From sebacic acid, 2ethyl hexanol and Polygiycol 200.

In the third table the lubricant had the following composition:

I 30% complex ester* sample E v 20% DOS 50% DNS '+3.6% Acryloid 710 1 purified phenol From sebacic acid, 2-etl1yl hexanol and Polyglycol 200.

TABLE 2 K. V., cs. at -40 F.

Additive Before After -65 7 soak F. soak (17 hours) Nil 5,740 14,450 2% Gatechol. l. 180 7, 060 7, 360 7, 340 2% Resorcino 7, 950 7, 870 1 2% 2,3,dihydroxy naphthalene 7, 510 7, 400 1% N acyl p-amino phenol 1 5, 830 6, 310 7, sec 7, 470 6, 300 6, 260 ample (e) insame blend: 5. 740 10,620 pyrogallol- 6, 610 6, 920 5, 405 o, 080 5, 305 0, 250 5,610 6, 990 5,965 6, 290 1% salicyl anilide 6, 241 7, 350 2% N N di-tert butyl p-phenylene diarnine 6, 245 9, 125

4 In the fourth table the lubricant had the following composition:

20% complex ester* sample D 20% DOS 50% DNS +3.6% Acryloid 710 1% purified phenol From sebacic acid, 2-ethyl hexanol and Polyglycol 200.

It will be seen that the aromatic nucleus seems essential and that other substituents such as halogens appear to result in ineffective compounds.

It will be seen that the additive used in the above example had a dramatic efiect in reducing the low temperature thickening properties of three distinct batches of ester lubricant that had themselves diverse properties in this respect. 1

The treatment 'With the salt of the strong organic base is preferably carried out by heating the blend containing more than 0.1%, preferably between 0.2% and 2% by weight of the salt, with stirring, to a temperature above C., preferably between C. and 190 C.,*for a time between 5 and 120 minutes, preferably 10 and'60 minutes, and then filtering the reaction mixture.

The mixture usually precipitates a small-amount'of 'a dark coloured resinous material and the colour'of the synthetic lubricating oil composition is improved. f

The treatment does not appear to affect, significantly, the viscosity of the blend at 100 F. or the viscosity index.

The following example illustrates one embodiment of the present invention.

Example nonyl alcohol, sebacic acid and polyglycol 200 (predominantly tetra-ethylene glycol) by forming the halfester of the polyglycol and the acid in a first stage, and

esterifying the acid product so formed with the monohydric alcohol in a second stage as described and claimed in our British specification No- 666,697. This blend was heated, with stirring, with 1% by weight of guanidine carbonate at C.- for 15 minutes. .A small-amount, comparable to the amount of added salt, of a dark brown resinous material precipitated and carbon dioxide was evolved. The reaction mixture was filtered.

The following table shows the effect of this treatment:

'Before After 1;

treatment treatment Initial viscosity at 40 F. (Centistokes) 11,500 11, 770

Viscosity at 40 F. after 17 hours storage at 40 F. (OentiStokes) 60, 000 12, 360 Colour '1. R 2% .13 Viscosity at 100 F. (Centistokes) 57. 8 61. 2

' The present invention may, of course, be applied to synthetic lubricating oil compositions which contain added materials such as, for example, anti-oxidants, antiewear agents and V1. improvers. What we claim is: I

' 1.- A process for improving the low temperature viscosity of asynthetic lubricating composition, said 'co'nr' formed with the monohydric alcohol in a second stage and a di-ester consisting essentially of di-nonyl sebacate, said process comprising adding to said blend in the range of 0.1 to 2.0 weight percent of a guanidine salt of an oxy acid, heating said mixture above 100 C. and filtering said mixture.

2. A process for improving the low temperature viscosity of a synthetic lubricating composition, said composition comprising a blend of 60% of a complex ester prepared from nonyl alcohol, sebacic acid, and a polyethylene glycol of a molecular weight of about 200, by forming a half ester of the polyglycol and the acid in the first stage, and esterifying the acid product so formed with the monohydric alcohol in a second stage and 40% of a di-ester consisting essentially of di-nonyl sebacate, said process comprising adding to said blend in the range of 0.1 to 2.0 weight percent of guanidine carbonate, heating the mixture so obtained to a temperature of 180 C., maintaining said mixture at said temperature for fifteen minutes whereupon a small amount of a resinous material comparable to the added amount of carbonate is precipitated and carbon dioxide is evolved, and filtering said mixture to remove said precipitate.

3. A process comprising adding to a synthetic dicarboxylic acid ester lubricant having a viscosity at 210 F. in the range of l to 20 cs., in the range of 0.1 to 2.0 weight percent of a guanidine salt of an oxy acid, heating said mixture between about C. and 190 C. for about 5 to minutes, filtering it to remove precipitated resinous material, and recovering a synthetic lubricant improved in color and in resistance to thickening upon storage at low temperatures.

4. A, synthetic lubricating composition improved in color and in resistance to thickening upon storage at low temperatures, formed by preparing a mixture consisting essentially of a synthetic dicarboxylic acid ester lubricant having a viscosity at 210 F. in the range of l to 20 cs. and in the range of 0.1 to 2.0 weight percent of a guanidine salt of an oxy acid, heating said blend between about 100 C. and C. for about 5 to 120 minutes andfiltering to remove precipitated resinous material. g

5. A synthetic lubricant improved in color and in resistance to thickening upon storage at low temperatures, formed by reacting a lubricant consisting essentially of a blend of a complex ester prepared from nonyl alcohol, sebacic acid, and a polyethylene glycol of a molecular weightof about 200, by forming a half ester of the polyglycol and the acid in the first stage, and esterifying the acid product so formed with the monohydric alcohol in a second stage and a di-ester consisting essentially of di nonyl sebacate Within the range of 0.1 to 2.0 weight percent of a guanidine salt of an oxy acid, heating the mixture so obtained above 100 C. and filtering to remove precipitated resinous material.

References Cited in the file of this patent UNITED STATES PATENTS 2,636,858 Jones Apr. 28, 1953 

1. A PROCESS FRO IMPROVING THE LOW TEMPERATURE VISCOSITY OF A SYNTHETIC LUBRICATING COMPOSITION SAID COMPOSITION CONSISTING ESSENTIALLY OF A BLEND HAVING A VISCOSITY AT 210*F. IN THE RANGE OF 1 TO 20CS. OF A COMPLEX ESTER PREPARED FROM NONYL ALCOHOL, SEBACIC ACID, AND A POLYETHYLENE GLYCOL OF A MOLECULAR WEIGHT OF ABOUT 200, BY FORMING A HALF ESTER OF THE POLYGLYCOL AND THE ACID IN THE FIRST STAGE, AND ESTERIFYING THE ACID PRODUCT SO FORMED WITH THE MONOHYDRIC ALCOHOL IN A SECOND STAGE AND A DI-ESTER CONSISTING ESSENTIALLY OF DI-NONYL SEBACATE, SAID PROCESS COMPRISING ADDING TO SAID BLEND IN THE RANGE OF 0.1 TO 2.0 WEIGHT PERCENT OF A GUANIDINE SALT OF AN OXY ACID, HEATING SAID MIXTURE ABOVE 100*C. AND FILTERING SAID MIXTURE. 